\documentclass{ctexart}
\usepackage{avanti}
\everymath{\color{Solarized-magenta}}
\pagestyle{empty} % 没有页眉和页脚

\tikzset{font=\large}

 % define the plot style and the axis style
\tikzset{base/.style={smooth,thick,Solarized-base01,draw=Solarized-base01}}
\tikzset{arrow/.style={->,>=stealth,base}}
\tikzset{curve/.style={base,Solarized-blue}}
\tikzset{nc/.style={base,circle}}
\tikzset{box/.style={base,rectangle,minimum size=20}}

\begin{document}

\begin{tikzpicture}

    \node [box,fill=Solarized-base2] (o) at (0,4) {输出层};

    \node [box] (a) at (0,2) {隐藏层};
    \node [box] (d) at (4,2) {延迟器};

    \node [box,fill=Solarized-base2] (i) at (0,0) {输入层};

    \draw [arrow] (i) -- (a) node [midway, draw=none, left] {$\xv_t$};
    \draw [arrow] (a) -- (o) node [midway, draw=none, left] {$\av_t$};

    \draw [arrow] (a) to [out=45,in=135] (d);
    \node [above] at (2,3.1) {$\av_t$};

    \draw [arrow] (d) to [out=225,in=315] (a);
    \node [below] at (2,0.9) {$\av_{t-1}$};

\end{tikzpicture}




\end{document}

